The present invention relates to a satellite communication antenna apparatus which can track a plurality of communication satellites at high precision and transmit and receive radio waves to and from them.
A conventional satellite communication antenna uses a parabolic antenna to transmit and receive radio waves to and from one communication satellite.
In recent years, a communication system is proposed which transmits and receives radio waves to and from, e.g., two satellites, among a plurality of communication satellites, located at the optimum positions for communication. Preferably, this satellite communication system tracks a plurality of communication satellites by changing its position such that its antenna unit is directed toward the positions of the communication satellites, and transmits and receives radio waves to and from the communication satellites.
One of satellite communication antennas used in this communication system uses a spherical radio wave lens and an antenna unit movable on an arcuate guide rail, and positions the antenna unit at a position opposite to the communication satellite through the radio wave lens, so that it can perform communication efficiently with the communication satellite.
The conventional satellite communication antenna described above has the following problems. If the antenna unit is driven along the arcuate rail, the mechanism becomes complicated, and position detection is difficult to perform.
As a driving force transmitting method, a ball screw method and belt method are generally employed. With these methods, however, it is difficult to move the antenna unit along an arc. If a ball screw or belt is added, the resultant mechanism becomes expensive. A guide or driving force transmitting mechanism made of a metal may undesirably disturb the intensity distribution of the radio waves to be transmitted and received. In order to transmit and receive radio waves to and from a plurality of communication satellites, a plurality of antenna units must be moved, leading to a further complicated mechanism.
As a position detection means, one is available that outputs an analog signal in accordance with the position of the antenna unit by utilizing a change in electrostatic capacitance upon movement of the antenna unit, as in a dielectric electrostatic sensor disclosed in Jpn. Pat. Appln. KOKAI Publication No. 6-196917. This method, however, lacks linearity, and cannot perform precise position detection.
As a countermeasure, one is available that detects the reception level of the radio waves from the satellite and performs position detection in accordance with the level, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 9-51220. According to this method, the antenna can always be set in a predetermined direction toward the position of the satellite. This method, however, cannot be used when radio waves from the satellite cannot be received.